Identification and Characterization of Nanoclays in Gamalama Volcanic Soil of Northern Maluku

Abstract

Clay minerals in Gamalama volcanic soil have not yet been identified thoroughly. The soil is estimated to contain nanoscale natural clays, such as halloysite or imogolite. The occurrence of nanoclays in the soil will support the development of many applications in nanotechnologies from nature. The objective of the present study was to characterize soil samples from five different locations around the volcano at three different depths from the soil surface. A total of 50 g of dry soil sample was stirred slowly in 300 mL of distilled water. Stirring was stopped after the addition of 10 mL of 30% H2O2 and then allowed to stand for 24 h. The small floating particles with dimensions of <2 μm were separated from the mixture and collected using a centrifuge at 4000 rpm (1790×g) for 30 min. About 5 g of solid sample was obtained for further characterization. X-ray diffraction results showed the presence of halloysite, allophane, and kaolinite. Morphology analysis by scanning and transmission electron microscopy of some representative samples showed short tubes 10–20 nm in diameter and 50–100 nm long with the halloysite structure. Halloysite was found at 70 cm depth from the soil surface at almost all locations. The surface area determined by the surface area analyzer using the BET equation was as much as 112.51 m2/g. This surface area is thought to be the largest ever determined for a natural nanoclay, paving the way for future application as catalytic or photocatalytic-supporting materials.

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“…For example, when coated ENM are released to the environment from nano-enabled products, these surface functionalizations can be lost and there could be no evident distinction with a natural NM with similar phys-chem characteristics [36]. The only point which is debatable is when ChatGPT mentions carbon nanotubes (CNTs) in volcanic ash because so far only halloysite or imogolite nanotubes (composed of inorganic minerals) have been identified in volcanic soils [37], not CNTs. It would be helpful if ChatGPT would provide the references because of the transparency and reliability of its answers, because then one could verify the source of information.…”